The invention relates to improvements in apparatus for filtering plasticized materials in extruding, injection molding and like machines. Apparatus of such character are disclosed in the aforementioned commonly owned U.S. Pat. Nos. 4,701,118 and 4,725,215.
European Pat. No. 02 50 965 A 1 corresponding to U.S. Pat. No. 4,752,386 granted Jun. 21, 1988 to Schulz et al.) discloses a filtering apparatus wherein rod-like carriers of filters for plasticized material are provided with rinsing or flushing channels which communicate with the outlet of the housing for the filter carriers. The carriers have chambers for the respective filters, and the flushing channels are disposed between the outlet of the housing and those sides of the respective filters which confront the inflowing plasticized material, i.e., that mass of plasticized material which is about to pass through the filter on its way into the outlet. Such communication between a chamber and the outlet is established when the corresponding carrier is caused to assume a cleaning or flushing position, namely when the chamber is sealed from the outlet. The flushing channels direct contaminated plasticized material into a collecting space or into the atmosphere.
The apparatus of the European patent is capable of expelling impurities or contaminants from those sides of the filters which confront the inflowing plasticized material. This is achieved by forcing plasticized material to flow counter to the normal direction of flow in the chambers so that the plasticized material traverses the pores, interstices, orifices or otherwise configurated openings of the filters in a direction counter to that in which the material normally flows from the inlet toward the outlet of the housing. A drawback of such apparatus is that the flushing channels contain stagnant bodies of plasticized material when the respective filter carriers assume their normal positions, namely those positions in which plasticized material flows from the inlet of the housing, through the filters in the chambers of the carriers and on toward and into the outlet of the housing. In other words, each carrier contains a column of stagnant plasticized material which is maintained at an elevated temperature (because the carriers are very hot) and is likely to undergo cracking. Decomposed plasticized material is then admitted against the clean side of the respective filter and must be forced through the filter on its way out of the filtering apparatus. Thus, even though the patented apparatus enables plasticized material to expel contaminants from the "dirty" sides of the filters, such expulsion of contaminants involves filling the chambers at the clean sides of the filters with decomposed plasticized material. When the carrier (wherein the chamber at one side of the filter is filled with decomposed plastic material) thereupon reassumes its operative position, decomposed material is expelled from its chamber and is forced to enter the outlet of the housing, i.e., it is compelled to enter the extruding or injection molding machine.